1. Field of the Invention
The present invention relates to psychometric, neuropsychological and neurophysiological tests for measuring mental acuity and more particularly to the use of electroencephalogram (EEG) recordings for such measurements.
2. Description of the Related Art
There is currently no method that quickly and objectively measures an individual""s overall cognitive ability. Nor is there a method that is able to do so on repeated occasions in order to measure changes in overall cognitive ability due to disease, injury, or other conditions affecting higher cognitive brain functions, or such changes due to remedial treatment. A person""s overall cognitive ability, often called xe2x80x9cgeneral intelligence,xe2x80x9d is considered an attempt to quantify analytic cognitive ability. It does not measure other types of intelligence i.e., creative and practical, or xe2x80x9cmultiple intelligencesxe2x80x9d i.e., linguistic, musical, bodily/kinesthetic, emotional, interpersonal and intrapersonal.
The presently available various psychometric tests of overall cognitive ability, such as the Weschler Adult Intelligence Scale (WAIS) or Raven""s Progressive Matrices, each suffer from one or more deficiencies. These deficiencies include cultural bias, subjective interpretation, excessive test length, high cost, and lack of assessment of the subject""s motivational factors in performing the test. Also, most test instruments lack multiple applications of the test that would be needed for repeated testing. Additionally, no psychometric test provides direct information about the subject""s actual brain function and hence supplies no information relative to the putative pharmacological action of a drug, disease, injury or therapy which is being studied. This lack of suitable tests is a major barrier to long term assessment of changes in an individual""s level of overall cognitive ability. This assessment is of paramount importance in evaluating the success of a putative treatment for any form of treatment affecting higher cognitive brain functions, for example drugs to aid memory in elderly patients. In principle direct measurement of brain functions underlying overall cognitive ability, by EEG measurements of brain wave activity, could overcome these deficiencies. Prior attempts at such EEG measurements, however, have not been fruitful because of two major shortcomings. First, there was the failure to measure brain activity while the subject performed a task taxing the subject""s mental processes, such as working memory, that are highly related to overall cognitive ability. Merely recording brain activity while the subject sits idly, watching a meaningless flashing light, or performing a task not requiring her or his full attention is insufficient to produce patterns of brain activity characterizing individual differences in overall cognitive ability or changes in an individual""s overall cognitive ability over an extended time period. Second, there was a reliance on single, overly simplistic measures of brain function derived from theoretical constructs without sufficient support from empirical data. For instance, although it may seem reasonable a priori that higher overall cognitive ability should be associated with faster brain processing, it is not necessarily true that a measure of the speed of brain processing is actually sufficient to characterize individual differences in overall cognitive ability.
In Schmidt et al., U.S. Pat. No. 5,339,826, the effectiveness of video-taped training material is tested using EEG. In one method, the student""s brain wave alpha and beta band activity is analyzed to determine attention and cognitive activity. In another method EP (Evoked Potential) responses are measured using multiple choice questions.
In Cohen U.S. Pat. No. 4,203,452 a single channel of EEG is measured in an attempt to ascertain if a student is undergoing short-term learning or long-term learning.
In Gevins U.S. Pat. No. 5,447,166 EEG signals are used to alter a computer program, i.e. present more or less difficult test material to the user.
Bennett U.S. Pat. No. 3,809,069 seeks to measure the intelligence of a subject using pulsed stimuli to evoke the subject""s responses, which are compared to the frequencies of responses of others.
These patents, and the other references cited, are incorporated by reference herein.
In accordance with the present invention, a novel method and system called xe2x80x9cNeurocognitive Ability Measurement Systemxe2x80x9d is provided for testing the brain activity of subjects while they perform a simple cognitive task in order to measure overall cognitive ability.
The main advantage of this system is that, by measuring neurological signals of basic cognitive processes underlying overall cognitive ability, it is able to determine a subject""s cognitive ability quickly, objectively, without cultural bias, and on repeated occasions. This differs from current psychometric intelligence tests that are lengthy, subjectively interpreted, depend in part upon culturally specific knowledge and are not designed to be used for repeated testing of the same person. The xe2x80x9cNeurocognitive Ability Measurement Systemxe2x80x9d also differs from prior attempts to use measures of brain activity to characterize cognitive ability in a number of essential respects. First, prior methods did not record brain activity while a subject performed a task engaging specific cognitive functions, such as working memory, that are highly related to overall cognitive ability. Thus, the prior measures were not specific to higher intellectual functioning. Second, prior methods only used single measurements of brain function to predict cognitive ability, and consequently had only a modest correlation with a subject""s overall cognitive ability. By contrast, the xe2x80x9cNeurocognitive Ability Measurement Systemxe2x80x9d combines several independent measurements of brain function and consequently produces a high correlation with a subject""s overall cognitive ability as measured with a standard psychometric test. Third, in estimating overall cognitive ability, prior methods that measured brain activity did not consider the speed or accuracy of a subject""s performance of a cognitive task, further restricting the test""s accuracy. The xe2x80x9cNeurocognitive Ability Measurement Systemxe2x80x9d combines measures of both brain function and task performance to achieve a more accurate prediction of a subject""s cognitive ability.
The system operates as follows: the subject is tested while performing a simple cognitive task as his or her brain waves are recorded. The subject""s overall cognitive ability (xe2x80x9cgeneral intelligencexe2x80x9d) is computed by combining task performance measures and brain wave measures according to a formula previously determined from a normative group of subjects of the same age range.
The system uses a digital computer workstation having a screen and a response input device, and an EEG device (electroencephalograph) to measure the brain waves of the subject. The EEG device also measures eye and scalp muscle activity and head movements in order to determine whether and how the brain waves are contaminated by artifacts. The system either removes such contaminants when possible or else discards the contaminated data. The subject is presented with a brief task on the screen that tests a fundamental cognitive function that is highly related to overall cognitive ability, preferably the function of working memory. (Working memory refers to the limited capacity to control attention and sustain its focus on a particular active mental representation for several seconds. This ability plays an important role in comprehension, reasoning, planning, and learning.) A subject""s behavioral responses and brain waves are measured as she or he performs a series of repetitions of easy and more difficult versions of the task. The subject""s brain waves are also recorded at rest for comparison with data recorded during performance of the task. A plurality of primary measures are computed from the data, preferably including: 1) the subject""s reaction time to each task trial; 2) the accuracy of the subject""s response to each task trial; 3) the amplitude of the subject""s EEG alpha band activity recorded over parietal and prefrontal cerebral cortical brain regions; 4) the amplitude of the subject""s EEG frontal midline theta activity; 5) the peak time of the subject""s fronto-central P200 and P300 averaged evoked potential peaks elicited by the task stimuli; 6) the peak amplitude of the subject""s fronto-central P200 and P300 averaged evoked potential peaks elicited by the task stimuli; 7) the amplitude of the subject""s frontal delta power associated with slow horizontal eye movements; 8) the amplitude of the subject""s posterior theta and delta powers; 9) ratios of the subject""s posterior theta to alpha power; 10) ratios of each of primary measures 1-6 and 9 between different locations on the scalp; and 11) measures of covariance, correlation or coherence of primary measures 3 and 4, and of the P200 and P300 amplitudes, between different locations on the scalp. Secondary measures are then computed preferably including: 1) differences in the primary measures between resting and the easy task version; 2) differences in the primary measures between easy and more difficult task versions; 3) differences in the primary measures between initial and subsequent repetitions of the task in the same session; and 4) differences in secondary measures 1 and 2 between initial and subsequent repetitions of the task in the same session. The preceding procedure of collecting and analyzing data is repeated over a normative group of subjects. Equations are then computed, preferably using a multiple regression or neural network algorithm. The equations consist of weighted combinations of some or all of the primary and secondary measures that best predict the overall Weschler Adult Intelligence Scale (WAIS) score of each member of the group. The output of these equations are called Neurocognitive IQ (NIQ) scores. The NIQs of a new subject are then determined by first measuring her or his behavioral responses and EEG while performing the same cognitive tasks, then computing the appropriate primary and secondary measures, and finally weighting them according to the equation determined from the normative group. If the subject has been previously tested with the xe2x80x9cNeurocognitive Ability Measurement System,xe2x80x9d the system can compare her or his current NIQs with prior test results to determine whether there has been a change.
Objectives of the present invention are to provide a method and system to:
1. Measure overall cognitive ability (xe2x80x9cgeneral intelligencexe2x80x9d) quickly, objectively, inexpensively and with minimal cultural bias;
2. Repeatedly measure overall cognitive ability of a subject in order to measure changes due to diseases, injury, fatigue, or other conditions, or treatment with drugs or other remedial therapies;
3. Repeatedly measure overall cognitive ability in order to measure changes due to training, learning, or use of drugs that improve brain function or slow the progression of diseases or conditions which affect higher cognitive brain functions.
It is a feature of the present invention to measure neurophysiological signals underlying overall cognitive ability while subjects are at rest and while they perform tasks engaging basic cognitive processes, such as working memory, that are predictive of overall cognitive ability.
It is a further feature of the present invention that the tasks used for testing do not depend on prior knowledge that is likely to be culturally biased, such as reading a particular language or making use of information derived from a particular cultural context.
It is a further feature of the present invention to use an easy and a more difficult version of a task for testing in order to apply a calibrated difference in mental workload to the subject from which the subject""s mental effort and amount of brain utilization can be estimated.
It is a further feature of the present invention to measure behavioral performance, such as performance accuracy and speed, while performing the cognitive tasks.
It is a further feature of the present invention to measure neurophysiological signals characterizing the subject""s mental effort and amount of brain utilization to perform the cognitive tasks.
It is a further feature of the present invention to measure neurophysiological signals characterizing the subject""s sustained focused attention while performing the cognitive tasks.
It is a further feature of the present invention to measure neurophysiological signals characterizing the subject""s neurocognitive strategy while performing the cognitive tasks.
It is a further feature of the present invention to measure neurophysiological signals characterizing the subject""s cognitive speed and transient focused attention while performing the cognitive tasks.
It is a further feature of the present invention to measure neurophysiological signals characterizing the subject""s alertness while performing the cognitive tasks and during the resting control tasks.
It is a further feature of the present invention to measure behavioral performance differences between performing an easy and a more difficult version of the cognitive task, and to measure differences in neurophysiological signals between resting, easy and difficult task versions, in order to measure how the subject""s brain and behavior respond to changes in mental workload imposed by the tasks.
It is a further feature of the present invention to measure changes in neurophysiological signals as a subject performs repeated trials of the cognitive tasks during one test session in order to characterize how quickly the subject""s brain adapts to the challenge imposed by the tasks.
It is a further feature of the present invention to measure differences in neurophysiological signals and cognitive task performance between initial and subsequent trials of an easy and a more difficult version of a cognitive task during one test session in order to measure how quickly the subject""s brain and behavior adapt to changes in mental workload imposed by the task.
It is a further feature of the present invention to compare measurements of neurophysiological signals and cognitive task performance between successive test sessions to determine whether the subject""s neurophysiological signals and cognitive task performance have changed due to an underlying clinical condition thus allowing detection of the aforementioned condition.
It is a further feature of the present invention to compare measurements of neurophysiological signals and cognitive task performance between successive test sessions to determine whether the subject""s neurophysiological signals and cognitive task performance have changed and continue to change when under the influence of an administered drug.
It is a further feature of the present invention to compare measurements of neurophysiological signals and cognitive task performance between successive test sessions to determine whether the subject""s neurophysiological signals and cognitive task performance have changed and continue to change under a regime of any non-drug related therapy meant to enhance such performance.
It is a further feature of the present invention to measure a multivariate combination of neurophysiological signals and cognitive task performance that, taken together, are empirically predictive of overall cognitive ability under well-controlled testing conditions.
It is a further feature of the present invention to determine overall cognitive ability score or scores by combining measurements of speed and accuracy of task performance with brain wave (electroencephalogram or EEG) measurements of alertness, focused attention, brain utilization, neurocognitive strategy, cognitive speed and transient focused attention, combinations of differences in the preceding measurements between resting and easy and more difficult cognitive task versions, and combinations of differences in the preceding measurements between initial and subsequent trials of the cognitive task during one test session.
It is a further feature of the present invention that the overall cognitive ability scores predicted by the multivariate combination of neurophysiological signals and cognitive task performance is the overall intelligence quotient as measured on a standard cognitive ability test such as the Weschler""s Adult Intelligence Scale.
It is a further feature of the present invention to test the overall cognitive ability of a subject by combining the above mentioned measurements according to equations previously determined on a normative group of subjects performing the same cognitive tasks and having the same neurophysiological and cognitive performance variables measured.
It is a further feature of the present invention to provide a method and system to determine the overall cognitive ability of a subject by measuring the subject""s brain waves while the subject performs a task that, for instance, engages the basic cognitive function of working memory.
It is a further feature of the present invention that the method and system supplies neurophysiological measurements that allow determination of the pharmacological effect of an administered drug on the aforementioned parameters of neurophysiological and cognitive performance, and thus aspects of any drug""s pharmacological action on the brain, including the ongoing assessment of such pharmacological action on the brain.